Some of you may recall the post I did on Spelunky, that wonderful game where everything--and I do mean everything will conspire to kill you. Dwarf Fortress is a similar game with one difference: while Spelunky once in a while, out of sheer pity, may allow you to win, Dwarf Fortress does not. Mercy, pity, remorse, Dwarf Fortress needs nothing of these things, and you may hope for none of them here.
Dwarf Fortress is the product of a single developer, who I believe is a math teacher. That alone should give you pause, but the motto doesn't really give a whole lot of room for interpetation. When the rallying cry of a community is that "Losing is fun!", then you know that the game's going to be a little more challenging than your average game of Halo.
The point of Dwarf Fortres is to construct a colony of happy, productive little dwarfs in a particular region of a preconstructed world. Among the challenges you face include goblins, trolls, titans, madness, more goblins, magma, aquifers, flooding, drought, famine, lack of beer, hippy elves, more goblins... I think you get the picture.
Since it is a free, independently developed game, the original graphics are limited to some pretty obscure ASCII characters. There are some graphics tilesets out there that can make it prettier, but at the moment it looks like an impenetrable wall of characters when you start. Weirdly enough, though, if you play long enough it becomes perfectly understandable before long. Graphics, however, are going to be the least of your worries.
To say that the interface for Dwarf Fortress has a steep learning curve is kind of like saying that Mount Everest is a little hard to climb. The understatement is a killer. The person making this game has planned out nearly everything, from how the water flows downhill to how magma flows. He has modeled how injuries to dwarves play out not only in the general "blows to the head kill you faster" sense but also to the "if this guy hits the dwarf in the hand, he may lose feeling in some of his fingers for a while" sense. Wind, migration patterns for animals, social dynamics between dwarves and even the possible difficulties in providing healthcare for your settlement are taken into account, along with whatever possible disasters they might cause.
The number of possible failures are numerous. One fortress might fall when a maddened carpenter slaughters half your population, leaving the rest to fall into mourning, starvation and frantic attempts to survive. Another might succumb to a devastating assault by a goblin horde. Yet another when you accidentally build a volcano in the middle of your settlement (yes, you can!), while another might fall apart simply because of a sudden famine that leaves your weakened dwarves too vulnerable to fight off the elements any longer. The list goes on, but every fortress is a frantic, futile effort to keep your dwarves alive until finally your settlement is brought to ruin.
Yet in spite of the difficulty of this game and the sheer complexity of its mechanics, Dwarf Fortress is incredibly addicting. You get to design every aspect of your fortress yourself, and you quickly become attached to the stubborn, frustrating creatures you command. The online wiki helps make things a little less frustrating, and the fact that the game is free certainly adds to its appeal. If you have a few days to spend on a puzzle with infinite creative variations, I highly recommend Dwarf Fortress. And if you take me up on that, good luck. Don't let the giant cave spiders bite.